A description of the functional coupling between membrane electrical events and the exocytotic release of hormones from endocrine cells is of key importance to understanding the physiology of secretion in endocrine glands. Little is known about the ionic mechanisms involved in excitation-secretion coupling in these systems beyond a requirement for extracellular calcium and the presence of regenerative electrical response in the cell membrane. The membrane permeability mechanisms likely responsible for the relevent electrical phenomena have yet to be determined. The principle objective of the proposed study is to characterize the changes in membrane permeability triggered by known secretory stimulants and/or inhibitors in individual anterior pituitary cells in tissue culture. The powerful voltage clamp technique will be applied to these cells using the new "giga-seal" methods for patch and whole cell recording. The separate ionic current components involved in action potential generation will be characterized in lactotrophs from fish, the GH3 pituitary tumor cell line, and several secretory cell types from rat pituitary. Measurements of both macroscopic and single channel currents will be performed and analyzed with respect to voltage-dependence, ionic selectivity, and gating kinetics. The effects of various secretogogues upon these discrete ionic pathways will be assessed in an effort to define their role in the hormone release process. In addition, the possible involvement of agonist-induced conductances will be examined during pharmacological block of voltage-dependent channels. An attempt will be made to correlate distinguishing characteristics of the conductances in certain cell types with their specific secretory function by immunohistochemical identification of individual cells following electrophysiological measurements. This research will hopefully lead to a clearer understanding of the molecular events underlying hormone release in response to secretogogue binding. It will also provide a framework in which to examine possible changes in membrane properties related to pathologies of hormone secretion in the anterior pituitary.